John Goodman as Babe Ruth was awful. Tony Perkins as Jimmy Piersall was just as bad, although I understand there was a left-handed/right-handed thing going on there.
Robt. Redford did well as Roy Hobbs, and Tom Sellick was understandably a believable Jack Elliott (Mr. Baseball).
In most cases, a male actor playing a professional athlete reminds one of the fact that these actors are the ones who were acting in the high school plays, rather than playing ball.